4 Acids and redox
OCR Chemistry A Exam-style questions
1 Lead(I ) oxide is made when lead reacts with oxygen according to the reaction
shown in Equation 1.1.
Pb(s) O2(g) PbO2(s) Equation 1.1
a i Identify, using oxidation numbers, the element that has been reduced.
(1 mark)
ii Explain, in terms of electrons, what is meant by reduction.
(1 mark)
b Lead(I ) oxide reacts with ice cold hydrochloric acid to produce lead(I )
chloride and water.
i Construct an equation for this reaction.
(1 mark)
ii If the reaction is done at higher temperatures, the lead(I ) chloride
decomposes to give lead(II) chloride and chlorine. Write an equation for
the decomposition of lead(I ) chloride.
(1 mark)
2 Two students are working together to prepare a 250 cm3 standard solution of
sodium carbonate. The method states:
Using a balance accurate to two decimal places, weigh out approximately
1.3 g of anhydrous sodium carbonate accurately.
Transfer to a small beaker and dissolve the powder in approximately 100 cm3
of distilled water. Transfer this solution to a 250 cm3 volumetric flask using a
funnel.
Make up to the mark using distilled water.
The students weighed the sodium carbonate and recorded the mass as 1.4 g.
a i Define the term anhydrous.
(1 mark)
, 4 Acids and redox
OCR Chemistry A Exam-style questions
ii Identify the error that the students made in the weighing of the anhydrous
sodium carbonate powder.
(1 mark)
iii One of the students suggested dissolving the powder in 250 cm3 of
distilled water and then transferring this solution to the volumetric flask.
He thought this modified method would save time. Identify the error within
this modified method.
(1 mark)
iv Suggest an improvement to the original method that would ensure that all
of the powder weighed was transferred to the volumetric flask.
(1 mark)
b Determine the mass, in grams, of sodium carbonate in 250 cm3 of a
0.0520 mol dm−3 solution of sodium carbonate.
Mass of sodium carbonate g (2 marks)
3 Hydrogen peroxide, H2O2, decomposes into water and oxygen when heated.
a i Construct an equation for this reaction.
(1 mark)
ii Deduce, by use of oxidation numbers, which element is reduced and
oxidised in this reaction.
(3 marks)
OCR Chemistry A Exam-style questions
1 Lead(I ) oxide is made when lead reacts with oxygen according to the reaction
shown in Equation 1.1.
Pb(s) O2(g) PbO2(s) Equation 1.1
a i Identify, using oxidation numbers, the element that has been reduced.
(1 mark)
ii Explain, in terms of electrons, what is meant by reduction.
(1 mark)
b Lead(I ) oxide reacts with ice cold hydrochloric acid to produce lead(I )
chloride and water.
i Construct an equation for this reaction.
(1 mark)
ii If the reaction is done at higher temperatures, the lead(I ) chloride
decomposes to give lead(II) chloride and chlorine. Write an equation for
the decomposition of lead(I ) chloride.
(1 mark)
2 Two students are working together to prepare a 250 cm3 standard solution of
sodium carbonate. The method states:
Using a balance accurate to two decimal places, weigh out approximately
1.3 g of anhydrous sodium carbonate accurately.
Transfer to a small beaker and dissolve the powder in approximately 100 cm3
of distilled water. Transfer this solution to a 250 cm3 volumetric flask using a
funnel.
Make up to the mark using distilled water.
The students weighed the sodium carbonate and recorded the mass as 1.4 g.
a i Define the term anhydrous.
(1 mark)
, 4 Acids and redox
OCR Chemistry A Exam-style questions
ii Identify the error that the students made in the weighing of the anhydrous
sodium carbonate powder.
(1 mark)
iii One of the students suggested dissolving the powder in 250 cm3 of
distilled water and then transferring this solution to the volumetric flask.
He thought this modified method would save time. Identify the error within
this modified method.
(1 mark)
iv Suggest an improvement to the original method that would ensure that all
of the powder weighed was transferred to the volumetric flask.
(1 mark)
b Determine the mass, in grams, of sodium carbonate in 250 cm3 of a
0.0520 mol dm−3 solution of sodium carbonate.
Mass of sodium carbonate g (2 marks)
3 Hydrogen peroxide, H2O2, decomposes into water and oxygen when heated.
a i Construct an equation for this reaction.
(1 mark)
ii Deduce, by use of oxidation numbers, which element is reduced and
oxidised in this reaction.
(3 marks)
